Clamping devices are well known and widely used within the manufacturing industry for holding different kinds of tools for machining of work pieces of various materials. The clamping device may optionally be carried on a rotatable spindle, for holding e.g. a drill or a milling tool, or be unrotatable for holding e.g. a lathe tool.
One advantage with a clamping device of this kind is that it allows for a quick clamping of the tool, simply by rotating the cam shaft by about 100° to 200°, which has to effect that the tool will be drawn by a large force into the mounting bore of the housing and thereby be securely held by the clamping device. Also the releasing of the tool can be easily and rapidly performed by rotating the cam shaft in the reverse direction. Normally, the bore of the housing as well as the tool holder shank are also made slightly conical such that they are tapering in an axial direction rearward from the tool. In this way the connection between the tool and the clamping device also can be made totally free from any play which has to effect that the tool will be held in an exact position which allows for high precision machining by means of the tool.
However, one disadvantage with prior art clamping devices of this kind is that the drawbar is made with a comparatively large cross-sectional dimension such that it cannot, with the desirable cross-sectional measures of the tool holder shanks frequently being used, be inserted through the bore of the housing from its forward end. The reason why the drawbar has to be made with such a large cross-sectional dimension is that the drawbar aperture has to accommodate a cam shaft having a cam formation of a sufficient size in order to provide the desired displacement of the cam shaft and the desired force reduction for the operator performing the rotation of the cam shaft during clamping and releasing. However, in order to ensure sufficient tensile strength of the drawbar to withstand the desirable forces by which the tool holder shank is drawn into the shank bore, the remaining leg portions of the drawbar surrounding the drawbar aperture must be made with a sufficient cross-sectional dimension. An example of a prior art design of a clamping device will be described more in detail in connection with the hereinafter detailed description.
Accordingly, in order to position the drawbar in place when assembling the clamping device, the drawbar has up to the present been inserted from the rear end of the clamping device or a shank bore sleeve has been mounted in the forward end of the clamping device after that the drawbar has been inserted into the housing from the forward end. One consequence of this is that the overall dimensions of the clamping device cannot be made as small and slim as desired. Another consequence is that the clamping device will comprise extra mounting details which will render the clamping device more expensive to manufacture, both in respect of material costs and costs for performing the assembling.